1. Field of the Invention
The present invention relates to, among interchangeable camera lenses which are removably mounted on a digital single-lens reflex camera, an interchangeable camera lens including a tilt/shift mechanism which can tilt and shift.
2. Description of the Related Art
A technique for an interchangeable lens has been discussed which is capable of, with respect to an imaging plane (image sensor), tilting an optical axis of a lens which is usually perpendicular to the imaging plane, or shifting (parallely moving) the optical axis of the lens which usually passes through the center of the imaging plane. These functions are collectively referred to as “capability of tilt/shift imaging”.
If such a tilt/shift function is used, arbitrary control of the depth of field and perspective correction can be performed. However, under such control, a problem also occurs. More specifically, by tilting or shifting the lens, an amount of light reaching the imaging plane or a light metering sensor decreases due to slant of the main light flux or vignetting of the light flux. Consequently, imaging with an appropriate exposure can be difficult.
In addition, when shifting is performed, an image height in a shift direction becomes substantially higher. Due to the effects of various aberrations and changes in a peripheral light amount, the image can look drastically different on a right and a left sides of the shift direction. Further, since the conditions for the range-finding sensor change, there is the problem that it is difficult to achieve an appropriate autofocus.
To resolve the above-described problems, Japanese Patent No. 3165433 discusses detecting the shift amount and the tilt amount, and selecting an exposure correction amount using a matrix table. Further, Japanese Patent No. 3165433 discusses a technique which may provide a tilt/shift lens with a revolving function (rotation function around the optical axis). In such a case, the exposure correction amount can be selected based on the shift amount, the tilt amount, and the revolving amount. When the revolving function is provided, the tilt direction and the shift direction (direction in an orthogonal plane to the optical axis) are fixed in a given relationship. If either of the tilt direction and the shift direction is detected, the other direction will also be known.
However, currently, assuming that imaging is performed in a great variety of situations, it is desirable that a user can freely change a relative angle between the tilt direction and the shift direction (angle in an orthogonal plane to the optical axis). In such a case, to calculate an appropriate exposure correction amount, in addition to a configuration for detecting movement in the tilt direction and the shift direction, a configuration for detecting a relative angle between the tilt direction and the shift direction also becomes necessary.